1. Field of Invention
This invention relates generally to the field of photography, and specifically to a positioning system for motion picture camera equipment.
2. Terminology
For the purpose of this discussion, certain terminology specific to the motion picture industry will be defined and referred to throughout.
Mitchell Mount: Standard within the American motion picture industry is a method of mounting a camera or camera head to a support platform which employs a male threaded stud of 2.75 inches in diameter, a corresponding aperture on the support media (tripod, dolly, etc.), and a female nut. The entire system is referred to collectively as a “Mitchell mount.” The male threaded stud is termed a “male Mitchell screw,” the aperture is termed the “female Mitchell mount” and the nut is a “Mitchell nut” or “tie down.”
Camera Dolly: a rolling platform which allows for the positioning of the camera.
Dolly Grip: This term is applied to the technician who is responsible for mounting the camera to the dolly and positioning the camera dolly while filming.
Composition: This refers to the elements within the film frame and how they are arranged spatially.
Slider: A linear track and bearing system used to position a camera while filming.
Speedrail®: Aluminum tubing of uniform diameter and the associated cast aluminum fittings which together are used to form structures suitable to supporting motion picture equipment.
Cheeseplate: Aluminum plate of various sizes which has been provided with a grid of ⅜ths inch diameter through holes drilled on 1 inch centers. These plates are used in conjunction with Speedrail® to mount camera and lighting equipment in many situations.
3. Description of Related Art
For artistic effect or simply to maintain desired frame composition, a motion picture camera must be able to move smoothly while filming. Historically, this requirement has been met by mounting the camera to a camera dolly which is in turn positioned by the dolly grip. The dolly grip acts under the direction of the camera operator, who views the frame composition through the camera's viewfinder.
Several problems arise when using such an arrangement. Principal among these is the fact that the operator has no direct control over the camera position and must rely on the dolly grip's judgment and intuition. The dolly grip usually has no means for viewing the frame composition directly, so he may be unaware if an undesirable situation arises; the obscuring of one actor by another, for example. Verbal communication between the dolly grip and the operator is considered disruptive to the actors' performance and is frowned upon. Furthermore, the inherent lag time between communication and action may negatively affect the desired result.
To address these issues, the use of a linear track and bearing system, or slider, has achieved great currency. Fundamentally, these sliders are longitudinal camera platforms which mount to the dolly and allow the camera operator to “slide” the camera along a longitudinal axis, thereby maintaining the desired composition of the frame without reference to the dolly. These sliders are constructed of commercially available linear rails bolted to aluminum plates or u-shaped channels. The camera mount is then provided with recirculating linear bearings which are sliceable along the linear rails. Means for attaching the base of the slider to the dolly is provided, usually in the form of a male Mitchell screw.
Although a useful tool, the slider in its accepted configuration presents certain difficulties. The linear rails are of fixed length and may not be adjusted. If a slider is found to be too short to provide the desired movement or too long to fit within the confines of the set, a completely different slider is required. Production companies therefore will rent or otherwise acquire more than one unit to cover the needs of the camera operator, incurring unwanted expense.
Another difficulty associated with the slider is its reliance on the dolly for support. The dolly is itself heavy and cumbersome in the tight quarters where a slider's usefulness is most appreciated.
A third difficulty concerns the accepted method of manufacture of the slider and the volume of expensive machining operations required to produce a slider. Inherent in the prior art is a large planar surface to which the linear rails are fixed. The majority of material in this plane serves no useful purpose as it does not contribute to the rigidity of the structure. This unwanted dead weight material is sometimes removed using a computerized milling machine or other means, but such operations are expensive. Furthermore, extensive drilling and tapping operations are required to provide suitable means for bolting of the linear rails to the aluminum body. These processes add considerably to the cost of production.